The present invention relates to an ocular optical system having a wide diopter adjustment range with good aberration compensation by only a slight movement of lenses.
In general, the adjustment of diopter is conducted by varying the distance from the eye point to the image to be viewed. In order to vary the distance, a viewed object is disposed on the inward or outward side of the focusing position of the ocular so as to produce an object as a virtual image or a real image at a predetermined position. For a single lens reflex camera, since the viewed object is fixed in position, the ocular or eyepiece is moved to obtain the same effect. Diopter is determined by the following equation: EQU S=-1000/(F.sup.2 /f.sub.B),
where S is the diopter, F is the focal length of the ocular, and f.sub.B is the distance from the viewed object to the focusing point of the ocular lens.
As is known from the above equation, if it is desired to make the focal length of the ocular lens long or to widen the adjustment rage of the diopter, it is required to lengthen the movement of the ocular. For a common viewfinder, since the space for movement of the ocular is restricted, it is difficult to widen the diopter adjustment range.
Accordingly, an object of the present invention is to provide an ocular optical system having a high performance with a wide diopter adjustment range even in a restricted space as in a camera.